1. Field of the Invention
The present invention relates to a process for remediating vaporous pollutants. More particularly, the present invention relates to a process for remediating vaporous pollutants using a carbon-coated substrate that supports pollutant-remediating microorganisms.
2. Description of the Prior Art
There are three common ways to remove vaporous or gaseous pollutants from gas- or air-streams. One common method is to pass contaminated gases over an absorbent, such as activated carbon particles, which absorbs the pollutants contained in the gases. However, this type of removal requires a large volume of absorbents and creates the problem of disposal or regeneration of the spent absorbents.
The second common method is to pass contaminated gases through a biologically activated sludge that contains microorganisms which can metabolize and remediate the pollutants. This type of bioremediation processes are disclosed, for example, in U.S. Pat. Nos. 4,544,381 and 4,894,162. These processes also have disadvantages in that they create a large volume of sludge that needs to be disposed of and the rate of remediation is limited by the solubility of the pollutants in the sludge.
The other common method is to pass contaminated gases through a bed of substrates in a bioreactor which carries microorganisms that degrade the pollutants contained in the gases. The prior art substrates used in this method have mainly been decomposable organic matters, such as peat, wood chips and other composts. For example, U.S. Pat. No. 4,662,900 discloses a variation of this substrate method. However, the use of decomposable organic matters as the substrates for supporting and carrying the bioremediating microorganisms may be disadvantageous in that the substrates decompose and settle with time. In addition, the organic substrates are not dimensionally stable, changing their dimension with the age of the substrate and the humidity level in the bioreactor. Such settlement and dimensional instability change the flow pattern of the gases fed through the bioreactor, creating undesirable flow patterns, and often create channeling that directs the influent gases to bypass substantial sections of the bioreactor, diminishing the efficiency of the reactor. In addition, the organic substrates do not have appropriate configurations to allow the gases to pass through without a substantial pressure drop, and the organic substrates tend to get clogged as the biomass density increases in the reactor. Therefore, the prior art bioreactors require a high inflow pressure feed the contaminated gases.
Therefore it would be desirable to provide a bioreactor for remediating vaporous or gaseous pollutants that is highly efficient and does not diminish in efficiency during its operation.